I sent this to Chicago DOT:

I travelled the Chicago Skyway today and noticed that they added "TO"
I-90 (EB) and I-90/94 (WB) banners above the reassurance route markers
along the route.  Did you remove the Skyway from the Interstate System?
I have a web page (http://www.theramp.net/n9jig/home.html) regarding
route numbers in Illinoius, and this would be an interesting tidbit.

Thanks!
Rich Carlson
http://www.theramp.net/n9jig/home.html

And I received this response:

Date: Thu, 19 Aug 1999 12:13:07 -0500
From: Frank BRINSKELLE <PW00...@CI.CHI.IL.US>
To: cw...@CI.CHI.IL.US, n9...@theramp.net
Subject: Re: Chicago Skyway/I-90

Mr. Carlson,

The Chicago Skyway Toll Bridge System was never incorporated into the
Interstate System and was incorrectly marked as interstate 90.  This point
was recently researched and no documentation was found.  This was recently
corrected by properly adding the "to " designation over the route marker.

Sincerely,
Frank J. Brinskelle
Skyway Capital Improvements Manager

First, I was suprised at the fast and fortwith response of Mr. Brinskelle.
Second, this is verrryy interesting...

--
Rich Carlson, N9JIG     n9...@theramp.net
Illinois Highways Page: http://www.theramp.net/n9jig/home.html